The background of the invention will be discussed in two parts.
1. Field of the Invention
This invention relates to a method and apparatus for bandwidth reduction, and more particularly, to a method and system for the transmission of high bandwidth signal information (e.g., video, high quality audio, and computer data) via low bandwidth media, such as telephone lines, radio frequencies, or for storage via computer RAM and ROM memories, optical and magnetic storage devices.
2. Description of the Prior Art
The telephone line is one of the most readily available and common methods of communication today. In addition to voice transmission, the telephone line is currently being utilized for data transmission, such as computer binary data. Telephone lines have been limited in transmission speeds, and, although transmission rates over telephone lines have steadily improved, the transmission rate is still not adequate for transmission of high quality images, and more especially, moving images. In many instances, such as with transmission over phone lines of digital data representative of a photograph or the like, the quality of the received image is poor. Improvements have been made in telephone lines by the use of fiberoptics, but fiberoptic use is not sufficiently prevalent at this time.
The most commonly employed method of bandwidth reduction is the time-scan technique, that is, pushing a lot of information through a small-capacity medium a little at a time until it is finally compiled at the receiving end. In the case of video picture phones (and facsimile machines), the prior art shows systems that require nine to thirty seconds to transmit one still picture, which, when received, is frequently subject to picture quality degradation.
U.S. Pat. No. 3,958,077, entitled "Picture Transmission Systems", issued to Ross on May 18, 1976, and discloses a system for transmitting video data in a smaller bandwidth than required for a conventional raster scanned frame, and employs a random or pseudo-random scan of a picture plane. The random scan is obtained in the X and Y directions of the picture plane by two shift registers, an X register and a Y register, connected serially, with random bit numbers entered into the first, X register. The random bit pattern is transmitted along with a video signal. The coordinates of the scanning spot are determined by the instantaneous content in the shift registers. Similar serially connected shift registers are used at the receiver, and the random bits, which are transmitted along with a video signal, are applied to the first of them. The coordinates for the current point to be scanned, as determined by the contents of the transmitting X and Y registers, are derived from the previous coordinates by shifting the complete contents of the X and Y shift registers one place to the right, losing the least significant bit in the Y register and injecting a random bit to the left or most significant location in the X register. After a number of shifts equal to the combined bit lengths of the X and Y registers (16 bits, for example) the receiver will be in synchronization with the transmitter no matter what the original content of the registers of the receiver.
U.S. Pat. No. 4,222,076, entitled "Progressive Image Transmitting", issued to Knowlton on Sep. 9, 1980, such patent disclosing a gray-scale image progressively transmitted over a narrow-band channel after the gray-scale values of all pictures elements (pixels) have been formatted into a hierarchial structure of picture subdivisions of successive sizes from entire image down to basic element values. Each formatted value is encoded as an approximate average of paired values. Transmission involves sending the primary value, representing the overall gray-scale magnitude, and following with successively split image values so that the entire image can be reconstructed at a receiver in progressively finer detail until the ultimate image results. The coding is nonredundant and full reconstruction is accomplished by transmitting the same number of bits that are required to send the image pixel-by-pixel and line-by line with the difference that an intermediate version can supply enough image detail for recognition. Unwanted images can be aborted at any intermediate stage, thus saving overall transmission time and effecting an equivalent picture compression when many images need to be examined in rapid succession.
U.S. Pat. No. 4,468,708. entitled "Combined Data Rate Reduction System", issued to Coleman, Jr. on Aug. 28, 1984, and discloses a method and apparatus for performing a reduction of the data rate of data stream for transmission through a transmission channel or recording and for subsequently reconstructing the original data stream upon receipt or during reproducing. The method and apparatus utilizes a combination of two processes, one of which eliminates or drops digital samples from the data stream to reduce the data rate for transmission and which subsequently reconstructs the original data stream using the unaltered and recovered digital samples to generate an interpolated value for each of the samples that had been dropped. The second process utilizes differential pulse code modulation for reducing the number of data bits per sample before sending the data stream through the transmission channel and for subsequently restoring the data to its original multi-bit form.
U.S. Pat. No. 4,628,344, entitled "Method and Apparatus for Encoding and Decoding Video", issued to Glenn on Dec. 9, 1986, such patent disclosing a method and apparatus for compatible transmission of high definition television signals in which existing low definition television receivers receiving the composite low and high definition transmission signal would display a low-definition television picture not inferior to present pictures, while a high resolution television receiver would receive the same signal and display a high definition picture. The system transmits low resolution video information at conventional frame rates, say 30 frames per second, while transmitting high resolution video information at a lower frame rate. The low and high definition video signals are derived in one embodiment by summing and averaging pixel luminance values, and subtracting the total of pixel values in some of the pixels in a group and the total of the pixel values of other pixels in the group. In another embodiment, the low and high definition signals, transmitted at regular and low frame rates, respectively, are derived by electronic processing of the video signal to produce signals representative of the low and high spatial frequencies, respectively, of the image to be transmitted.
U.S. Pat. No. 4,633,296, entitled "Omission and Subsequent Estimation of Zero Sequence Coefficients of Transformed Digitized Images to Facilitate Data Compression", issued to Cham et al, on Dec. 30, 1986, and discloses a method of transmission or storage of a television picture which involves dividing it into a plurality of blocks, subjecting them individually to a two-dimensional unitary transformation, transmitting or storing the transform coefficients and reconstructing the original blocks by the use of the inverse transformation. To reduce the data rate, the zero frequency (D.C.) coefficient is omitted for most or all the blocks, and the mean levels of the reconstructed blocks are adjusted to reduce visible brightness changes between them.
U.S. Pat. No. 4,672,444, entitled "Method for Transmitting a High-Resolution Image Over a Narrow Band Communication Channel", issued to Bergen et al, on Jun. 9, 1987, and discloses an image transmission method which analyzes the spatial-frequency spectrum of a high-resolution image into a low-pass remnant subspectrum band having a nominal high-frequency cutoff below that of one or more other spatial frequency bands, and separately transmitting each band, starting with the remnant band, over a narrow-band communication channel from a transmitter to an image display at a remote receiver.
U.S. Pat. No. 4,694,336, entitled "Digital Data Transmission Method", issued to Keesen, et al, on Sep. 15, 1987, such patent disclosing a method for transmitting digital video signals wherein spectral values of a scanned scene matrix are sorted according to magnitude, and the magnitudes of the spectral values then transmitted in succession, beginning with the greatest value. If the spectral values have been sorted according to magnitude, the magnitude of a spectral value always provides preinformation as to the magnitude of the next following spectral value.
U.S. Pat. No. 4,703,348, entitled "Picture Transmission System Using Secondary Differential Variable Sampling Rate Coding", issued to Yuasa et al, on Oct. 27, 1987, and discloses a picture transmission system which is adapted to code picture data by a variable sampling rate coding system to transmit the same. Picture data are stored in a frame memory of a transmission area so that differential values between that data and predictors from a predictive circuit are obtained by a subtracter and compression-coded by a variable sampling rate compression circuit for transmission. The compression-coded differential values are expansion-decoded by a variable sampling rate expansion circuit so that original differential values are supplied to an adder, which adds up the differential values with predictors, to produce predictors for subsequent sampling points. In a receiving area, transmitted codes are expansion-decoded by a variable sampling rate expansion circuit, so that the decoded values are added up with predictors from a predictive circuit by an adder to output the original picture data. Preposition prediction and variable sampling rate decoding are thus combined to enable, in the receiving area, automatic correction of compression/expansion errors caused in the transmission area.
In such prior art methods, when utilizing low bandwidth transmission media, a long time is required to send even a still image, with a full motion real time video image being highly impractical. The video transmission of color images is likewise highly impractical, and transmission of any image is prone to interference and distortion. present prior art attempts at video transmission are incompatible with existing video transmission systems, and the expansion of prior art system capabilities are impractical or non-existent.
In accordance with an aspect of the invention, it is accordingly an object of the invention to provide a new and improved method and apparatus for enabling high bandwidth information to be transmitted nearly instantaneously via low bandwidth media (or stored) with virtually no degradation of quality.